Heat resistant alloys

ABSTRACT

An aluminum-magnesium-silicon alloy with the customary additions for the production of parts such as cylinder heads, for resisting high alternating stressing and also high thermal stressing, wherein the improvement comprises the presence of grain-refined Mg2Si and a component for reducing the solubility of hydrogen.

O United States Patent 1 1 11 1 3,868,250

Zimmermann 1 Feb. 25, 1975 HEAT RESISTANT ALLOYS 3,279,915 10/1966Fujisawa et a1. 75/147 3,392,015 7/1968 Badia 75/147 [75] Invent: 'F3,429,695 2/1969 Nakamura et a1. 75/147 Grlmmlmghausem Germany 3,514,2865/1970 Unai et a1. 75/147 3,666,451 5/1972 [73] Asslgnee' Meschede'Ruhr3,698,890 10/1972 Bewley 75/147 Germany [22] Flled: June 1972 PrimaryExaminerW. Stallard [21] Appl. No.1 260,556 Attorney, Agent, orFirm-Spencer & Kaye [30] Foreign Application Priority Data June 14, 1971Germany 2129352 [57] ABSTRACT An aluminum-magnesium-silicon alloy withthe cus- [52] [1.8. CI 75/147, 148/3, 148/159 tomary additions for theproduction of parts Such as [5]] '9 Cl Czzc 21/04 Czzf 9 Fozf cylinderheads, for resisting high alternating stressing [58] held of Search75/147, l48/;,9l593, and also high thermal stressing, wherein theimprove ment comprises the presence of grain-refined Mg Si d a c m o entf0 ed cin the sol bilit ofh dro- [56] References Cited 22 O p n r r u gu y y UNITED STATES PATENTS 2,186,394 1/1940 Spitaler 75/147 9 Claims, 3Drawing Figures ALTERNAT1NG LOAD NUMBER lei/9 TOTAL 5.14

1 TOTAL 7.4

5 FREE Mg 0 MEASURED VALUES FROM TABLE 8 0 AVERAGE VALUES FROM TABLE 8 QAVERAGE VALUE FROM TABLE 7 OTHER ALLOYING COMPONENTS TABLE 8 0,98 7,00/a 51' 0,89 0,92 Mn .50 0,55 (u 0.75 /u Ti 0,33 -a14$ /0 Fe 0,4104% BeBALANCE Al n.b. NOT DETERMINED TABLE 7 M1. "/0 Ti 9'0 Be BALANCE AZFEHZSIBYS SHEET 1 BF 2 7400 %/v TOT. 7300 S3 1100 m g 7000 Z 2 .900 8800 g be O E 600 M1 TOTAL 5.|4 g m E 400 300 200 0 1w Z9 TOTAL 7.4

o s 5 FREE Mg 0 MEASURED VALUES FROM TABLE 8 Q AVERAGE VALUES FROM TABLE8 @i AVERAGE VALUE FROM TABLE 7 OTHER ALLOYING COMPONENTS TABLE 8 TABLE7 0,98 7,00 0 51' 0,94 0,99 /0 51' 0,89 0,92 /0 Mn 0.36 %/"/n 0,56 0,55(a 0.5.2 0,55 Cu 0,75 /0 Ti n. b. "/0 72' 0,33 -a4$ /oFe OAS-0,45%0,0049% Be n. b. %Be BALANCE Al BALANCE AZ n.b. NOT DETERMINEDPATENTEDrmmqm K SHEET 2 0f 2 FIG. 2

3.0 3.5 4.0 4.5 5.0 5.5 do 615 in %/1 FIG.3

1 HEAT RESISTANT ALLOYS BACKGROUND OF THE INVENTION The presentinvention relates to AlMgSi alloys with the customary additives and to amaterial thereof for the production of parts resisting highly cyclicloads and high thermal stresses, to the use of such alloys and ofmaterials thereof for heat-resistant parts, and to components made ofthese materials.

As a consequence of the higher requirements placed on a wide variety ofdifferent designs at the present time, metallic materials must withstandhigher stresses as well. These higher stresses of materials occur atlower and higher temperatures. Changes in the composition of alloys havebecome, therefore, necessary. Some alloys, among these theheat-resistant aluminum-magnesium-silicon alloys, represent anexception. They have been cast for decades in the same composition.

Investigations for an improvement of aluminum-magnesium-silicon alloyswere made almost three decades ago. These experiments relatedparticularly to the improvement of the age-hardenability of alloys with3% magnesium and 0.8% silicon. Through an addition of cerium themagnesium-silicide could be grain-refined. With further additions of0.8% zinc and 0.8% manganese alloyed together with cerium, a furtherimprovement was obtained which was, however, not so distinct as thateffected by the addition of cerium. This alloy has not been used.

Later, others carried out extensive experiments with extrudedaluminum-magnesium-silicon alloys in order to make the quasibinary, theternary and the beloweutectic compositions usable for heat-resistantpurposes. These experiments were not continued although also here thehot-strength inherent in aluminummagnesium alloys was noted and could beimproved by other alloying constituents.

These and other numerous experiments have led to the use ofaluminum-magnesium-silicon alloys, containing: 2-5.5% magnesium; -l.5%silicon; 00.6% manganese; 0-0.20% titanium, balance aluminum. Forheat-resistant purposes, mainly for use as cylinder head material, analuminum base alloy with the almost equal composition, used by allfoundries, of 4.8 5.5% magnesium, 0.8 l.2% silicon, 0.4 0.6% copper, theabove manganese content range, balance aluminum, was normally delivered.As per agreement with the purchaser, small quantities of beryllium weresometimes added to these alloys for inhibiting oxidation.

The ranges for the magnesium and silicon contents of these alloys permita wide variation in the quantity of magnesium silicide which can beformed. Furthermore, magnesium not combined with silicon is found in thealloys. This is shown in Table 1.

Table l-Continued Combined and Uncombined Magnesium SUMMARY OF THEINVENTION An object of the invention is to provide analuminum-magnesium-silicon alloy especially resistant to thermalfatigue.

This as well as other objects which will become apparent in thediscussion that follows are achieved, ac cording to the presentinvention, by an aluminum-magnesium-silicon alloy having grain-refinedMg Si and a component for reducing the solubility of hydrogen.

GENERAL ASPECTS OF THE INVENTION Toward the end of improving the alloysmentioned in the above BACKGROUND OF THE INVENTION, numerous experimentshave been made. These experiments were based on the working hypothesisthat aluminum-magnesium-silicon alloys for withstanding high stresses,in particular for withstanding alternating thermal stresses, mustpossess magnesium and silicon contents equilibrated to each other, andthat the free magnesium content umcombined with silicon must not exceedbeyond limits the solid solubility of magnesium in aluminum at roomtemperature.

Especially the use of the alloys mentioned in the BACKGROUND OF THEINVENTION for cylinder heads gave rise to the recognition that crackingcaused by the temperatures prevailing in the combustion chamber occursearlier at higher magnesium contents. A reduction of the magnesiumcontent to lower concentrations should also be of advantage forincreasing the solidus point of the alloys.

Besides establishing the influence of magnesium content, numerousinvestigations were made for establishing the influences of variousother alloying constituents. Prior to casting, the melts wereextensively degassed and only such elements were added, the addition ofwhich was known not to increase the solubility of hydrogen. Furthermore,the solidus points in the aluminum-magnesium-silicon system were not tobe decreased considerably, and in addition the grain refinement of thestructure was to be improved. Combined with the component for reducingthe solubility of hydrogen, it is important for obtaining the bestgrainrefinement in the Mg Si, i.e., for maximizing the fineness of theMg Si grains, that an extra measure be taken to assure no hydrogenevolution occurs during the time that the alloys are cooling from themolten condition to solidification to disturb the formation of a finemicrostructure. Such evolution is prevented by the intensive degassingat the time of casting. An equilibrium condition, under which nohydrogen evolution occurs, is obtained right at the time ofsolidification. This equilibrium condition corresponds to a certainmaximum amount of hydrogen dissolved in the melt at the time of casting.

lt was found that, when casting aluminum-magnesium-silicon alloys inpermanent molds having a temperature of 300 C, a finer distribution ofMg Si is obtained, the smaller the magnesium content of the alloy isthat is not combined with silicon, and that through an increasedmanganese content in the absence of cerium and zinc, a still finer Mg Siis obtained which at low magnesium content is recognized only at a veryhigh magnification microscopically as a very fine precipitate. Theinfluence of manganese on mechanical properties is consequentlyoutstanding at room temperature and elevated temperatures as shown inTable 2. The tensile test specimens of Table 2 were subjected to astabilizing annealing before testing. The stabilizing annealing causes amajor separating of solid solution crystals into separate phases andthus represents a softening anneal. Growth changes are prevented bythis. Decisive The specimens for obtaining the data specified in Table 2had a length of 22 cm and an original diameter of 2.2 cm over the wholegage length. They were made by chill casting at casting temperatures ofapproximately 720 to 750 C. The diameter over the gage length wasobtained by turning on a lathe from the as cast diameter of 2.2 cm to1.6 cm. The castings had a riser over their entire length. The mold,open at the top, was filled from one side through a gate. The chill washorizontal and had a temperature of 300 C.

The addition of manganese should not exceed the maximum solid solubilityin the aluminum-manganese system, but it should also not be lower than0.6%.

The grain refining of the structure of Mg Si through the action ofmanganese has nothing in common with the forming of pointed,needle-shaped iron aluminides by manganese in aluminum-silicon-alloyswith low magnesium-contents from up to approximately 0.6%. It is truethat in Al-Mg-Si alloys with Fe-contents of isamajor stabilizing againstthe effects oflater heating. 1.25%, Mg Si can be refined by highermanganese- When used, the material experiences no further contents, buta forming of the iron aluminide into a changes. The stabilizingannealing effects an annealing, multi-substance compound cannot occur asis the case a stabilizing, and a stress relieving. with aluminum-siliconalloys. These alloys have low In the Tables, the following symbols areused: elongation and strength properties, as shown in Table 0 yieldstrength 3. 0,, breaking strength The pointed iron aluminide structurefound in the 5 elongation aluminum-magnesium-silicon alloys of Table 3is not HB Brinell hardness. prevented in the ternary aluminum-siliconmagnesium Table 2 Charge Analysis in Tests at 20C Tests at 300C Tests at400C No. kp"/mm 7r kp"/mm kp' lmm 7c kp*/mm Mg Si Mn Fe 0' 17B 5 HB (701B 5 11.2 's .5

Avg. value 7.7 17.1 6.1 54 5.9 8.6 62.1 2.8 4.5 65.0

Avg. value 20.7 14.6 56 5.6 9.3 38.1 4.1 6.2 78.0

Avg. value 10.1 21.6 6.5 64 7.4 11.1 27.3 4.1 6.2 84.0

Avg. value 12.5 26.7 9.6 70 8.9 12.7 48.6 5.3 7.8 83.4

Avg. value 13.0 23.3 5.2 72 9.6 13.8 21.8 4.1 6.7 115.2

Avg. value 13.7 23.5 4.4 9.5 14.0 20.5 5.1 7.9 97.0

p ponds Further concerning Table 2 and subsequent Tables herein, thetest bars had a gage diameter of 16 mm and a gage length of 80 mm, i.e.,5-fold diameter. The elongation measured in the tensile testing machineduring the tension test until break of the test bar is the elongation 8stated in per cent of the original length of 80 alloys withapproximately 13% silicon and 6% magnesium by an increased addition ofmanganese. Such experiments show in regard to the strength propertiesalso no outstanding technical progress for a combination with manganese;they show also that in an application of manganese in the presence oflarge quantities of silicon and larger quantities of magnesium theeffect of manganese is not comparable to that in aluminumsilicon alloyswith up to 0.6% magnesium or without magnesium. See Table 4.

shows the improvement of strength properties caused by manganese inalloys lying approximately in the melting valley between the ternary,magnesium-rich and Table 3 Charge Analysis in Tests at 20C Tests at 300CTests at 400C No. kp/mm kp*/mm kp/mm 7r ltp/mm Mg Si Mn Fe (T 5 HB 0.2's s 0.2 n s Avg. value 8.8 17.4 3.6 57 5.3 9.2 44.5 2.9 5.0 80.0

Avg. value 9.3 16.2 2.5 63 5.5 10.3 10.4 3.6 6.5 65.0

Avg. value 10.6 22.6 4.9 71 8 3 12.1 37.9 4.1 6.7 98.2

Avg. value 10.4 18.5 3.0 69 8 5 l2 3 7.3 4.2 7.2 73.4

Avg. value 12.4 21.5 3.4 76 9.4 14.0 14.9 3.6 6.2 64.6

Avg. value 14.0 18.3 1.5 87 9.2 14.2 4.9 4.1 7.9 83.2

' p ponds Table 4 Charge Analysis in 7: Tests at C Tests at 300C Testsat 400C No. kp"/mm 7r llfp /mm kp"'/mm 7: kplmm Mg Si Mn Fe 0' a, 8, B(T a, 5 a o 8 Avg. value 9.5 16.9 2.9 59 3.8 7.6 11.6 2.4 5.0 20.0

Avg. value 10.7 17.0 2.2 67 5.6 9.2 11.2 2.7 4.2 20.0

Avg. value 10.7 11.9 0.9 70 3.0 8.8 1.8 2.9 64 3.0

Av. value 10.6 14.2 1.6 71 6.3 8.4 3.4 3.2 5.8 7.2

' p ponds After these investigations it was, therefore,astonishsilicon-rich eutectics of the aluminum-siliconing that at veryhigh magnesium-contents of approximately 9 10% and silicon-contents ofapproximately 3% at free magnesium-contents between 3 and 4% (magnesiumnot bound to silicon). also at higher ironcontents of 1.20%,iron-needles no longer occur, insofar as higher manganese-contents wereadded. However, in the presence of high quantities of iron, noconsiderable changes of strength properties have been caused. 1n thealloys with low iron-contents there is found by the manganese alloying,besides a strong refining of grain structure, a considerable increase ofstrength properties in connection therewith. Table 5 magnesium systemand preferably on the side rich on magnesium, and which havesilicon-contents lower than those of the quasi-binary eutectic with 13%Mg si. Preferably silicon-contents between 2.5 and 4% and at most 11%magnesium should be alloyed in the presence of manganese.

The investigations were extended to alloys with silicon-contents of 2%and magnesium-contents of 4%. The strong refining of Mg Si by manganeseis obtained here as well. I

With a Cu-content of 1% both in alloys poor on manganese and rich onmanganese, Mg Si is coarsened again. 1t is most coarse in the alloyspoor in manganese. Table 6 shows that a Cu-content increases strengthproperties, but that elongation properties are strongly decreased. Thestrength properties of Cu-free alloys with their highermagnesium-contents not bound to silicon, were not attained. Atapproximately 4% magnesium and 2% silicon, the alloy contains only 0.55%magnesium not bound to silicon. The machinability of castings from thesealloys is worse.

Further results were obtained on investigation of the influence ofnickel. Similarly to manganese, nickel contents of about 1% in aluminumshow the lowest hydrogen solubility in the molten state. Thiscomposition was, therefore, also selected for alloying investigations.It was found that contrary to copper. a 1.5% nickel content gives a veryfine magnesium-silicide and that the magnesium-silicide coarseninginfluence of copper is neutralized in the presence of nickel.

The investigation of tearing strength properties showed that thestabilized alloys, when the magnesium content exceeds 4%. possess lowelongation properties. and that the aluminum-magnesium-silicon alloysmust contain, in the presence of nickel and/or larger quantities than0.2% copper, less than 4% magnesium.

Table 5 Charge Analysis in 7: Tests at 20C Tests at 300C Tests at 400CNo. kp lmm kp lmm kp"/mm kp"/mm Mg Si Mn Fe a o 8 HB 0,, 6 01, 0,, 8

Avg. value 14.9 24.4 2.7 92 8.8 13.2 25.7 3.6 6.1 74.8

Avg. value 18.1 27.3 2.6 96 11.7 15.9 24.5 4.8 8.5 61.6

Avg. value 12.0 20.0 1.9 79 8.7 12.8 27.5

Avg. value 13.9 25.3 2.8 85 9.4 13.5 21.8

Avg. value 15.8 25.0 3.3 96 9.3 14.6 19.7 4.1 7.4 83.6

Avg. value 18.1 24.1 2.3 103 10.8 16.2 5.9 5.1 8.1 65.2

p ponds Table 6 Charge Analysis in Tests at C Tests at 300C No. kp"lmmkp"'/mm kp/mm Mg Si Mn Cu Fe M a 8,, HB 0' 0' 6 Avg. value 8.1 17.7 5.454 4.4 7.7 39.2

Avg. value 8.7 18.6 4.9 4.9 7.5 52.0

Avg. value 10.3 18.4 3.0 65 6.0 9.1 35.4

Avg. value 10.8 19.9 3.4 68 6.1 9.6 39.6

' p ponds BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a graph ofalternating load number versus the percentage of free magnesium in analloy.

FIG. 2 is a graph of the percentage of silicon in an alloy versus thepercentage of magnesium and shows the field of free magnesium contentsbetween I and 3%.

FIG. 3 is a cross section through a portion of an aircooled cylinderhead according to the invention.

.DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred elements forreducing the solubility of hydrogen in the melt above 700 C aremanganese and nickel.

The available results were applied to investigations of cylinder heads.The quality of service to be expected from an alloy used to make acylinder head was measured in terms of "alternating load number." whichis measured as follows.

On a heatable and coolable test stand, those portions of a cylinder headas are most endangered. being nearest to the combustion chamber. areheated for approximately 60 seconds from a temperature of I to 300 C andthen cooled in 60 seconds to I00 C again. This effects a change of load.The test on the test stand is carried on until crack formation and thenon until the crack has progressed through the wall where it is located.The number of load changes supported by the cylinder head until crackformation and until crackthrough yields alternating load numbers, whichserve as an indicator of the ability to resist thermal fatigue.

FIG. I shows among other things the alternating thermal stress tests ofcylinder heads made of the customary alloy AlMg5SilCu0.5 per Table 7.The cylinder heads of Table 7 were taken from the normal production in aperiod extending over several months. There resulted an averagealternating load number of 716 until crack formation and 769 untilcrack-through.

Cylinder heads cast from the material of the invention and showing afine grain structure were likewise tested. FIG. I and Table 8 show theresulting alternating load numbers. It can be concluded from theinvestigations that with a silicon content comparable with the customaryalloy. and with the customary addition of 0.5% Cu, alloys with highmagnesium contents have a considerably shorter operating life even withan additional manganese-alloying. In comparison with the results for thecustomary alloy (see FIG. I and Tables 7 and 8). the alloys with highermanganese content show a distinct improvement. The graph in FIG. I showsan almost linear dependence between alternating load number andmagnesium content and the possibility of a maximum improvement of I00%by the invention. The alloy used for cylinder head No. 3 in Table 8 andFIG. I possesses a free (i.e., not present in Mg si) magnesium-contentof approximately 5.7%; the alloy of head No. 2 has a freemagnesium-content of 3.77%; and the alloy of head No. I has a freemagnesiumcontents of only 2.85%. The alloys of heads No. 4 and No. 5 inTable 8 contain only about 0.9% free magnesium. The alloy of head No. 5endures after the additional alloying of manganese considerably higherthermal loading. Comparison with the alloys of Table 7 shows the highthermal stress endurance obtained by the reduction of the free magnesiumcontent. The free magnesium content of the alloys Nos. 4 and 5. being0.9%, is very low. The machinability of these alloys was worse on aproduction line. The free magnesium contents should be more than We.

The alloys of the invention can also be used as wrought material, if theSi-content is at least 1%.

All investigations show that the free magnesiumcontents of thealuminum-magnesium-silicon alloys for obtaining high endurance,specially against alternating thermal stresses, should be between I and4.5, preferably at 3.0%, a decrease of free magnesium to less than 1%being possible only for castings that are machined with special toolsadapted to the alloy. In the presence of more than 0.6% Mn the preferred3% free magnesium can go up to about 4.5%.

n.b. I not precisely determinable Table 8 fiyylinder Head Analysis in Zlclterriating load Mg 51 Mn Cu Fe Ti Be C 'ick Crackformation through I4.55 0.99 0.91 0.50 0.42 0.15 0.004 1450 I600 I350 1500 4 4.4 2.08 0.020.17 0.20 0.15 0.004 I040 60 930 I030 n.b. H

5 4.3 L88 0.78 0.15 0.21 0.15 0.004 I380 I590 I380 I420 I360 I410 1|.b.not precisely determinable During the further development of the alloysof the cylinder head in FIG. 3 from an alloy poor in mangainvention andof their applicability. it has been estabn e ha i thg composition lishedby thennal alternating stress investigations that, 03% M within therange of the limits of the invention. alloys 51% Mg with the followingalloying constitutents have particu- [3% Si larly favorable propertiesfor enduring high- 004% Be temperature alternating stresses and aparticularly low b I M d t t t I cracking-tendency in engine operation:a an cus (imary con amman ected to an alternating thennal stressrnvestrgatron after cooling the permanent mold with about 700 cm 70% MsH O in the area of the spherical cap ll. The cooling 8:: I a was carriedout by flowing the water through a metal 38:83?? mold core abuttingagainst the spherical cap I1 and other damn having cylinder insertsprotruding into the inlet channel will however 015% maximum l2'and theoutlet channel 13. The cooling effect pro- -vided by the cylinderinserts provides an additionallymfzztirr'isiiizlutmlgltzmnl;rlductgaozzgyn 0 improved microstructure inthe web 14, which is the silicon be contained in the alloy. A specialimportance rnost highly stressed portronof the head. The alterna tis. inhis insmnce attributed to the proportioning of mg load number wasapproxrmately 450 for the start of he manganese on which the increase ofcrack resisv crackrng of theweb area between the Inlet and outlet lancein engine operation depends channels. add tionally In FIG. 3. axes 15 16and l? are Thc p 1 alloy sckcdon results in panicularly 4 axes ofcylindrical symmetry for. respectrvely, the Inlet favmablc mechanicalpropcnies But a" anoys both channel 12. the spherical cap II. and theoutlet chanthose numed first. and those selected now, yield especiallyimproved mechanical properties and to the pres- EXAMPLE 2 ent time. thebest crack resistance-against temperature changes. if the endangered orhighly stressed areas of Cylmde' headsj of the alloy m Exa'rfple l thecast body are subjected during the solidification to showed bemg f wnhInc's m a cooling additional to the cooling received by other same analemamg load number of areas of the bod The behavior of allo free ofmanganese shows in cylinder heads 30 to 50 of the durabil- EXAMPLE 3 ityachieved in cylinder heads made of alloys contain- Cylinder heads of themanganese rich alloy with the i manganm, composition FIG. 2 shows therange of preferred alloy composi- Mn tions wherein only I to 3% freemagnesium (not bound 6o 44% g to silicon) is present. 19% Si Furtherillustrative of the invention are the following 0.004%- Be E l balanceAl and customary contaminants, were subjected, after cooling as inExample 2. to an alternating EXAMPLE I 5 thermal stress test and yieldedan alternating load num- Cylinder heads of the type illustrated byair-cooled ber of [.550 to crackthrough.

EXAMPLE 4 Under a more aggravated alternating thermal stress testconsisting of a more rapid change of heating and cooling, cylinder headsaccording to Example 2 gave the reduced alternating load number of 650.

EXAMPLE 5 Cylinder heads from alloys according to Example 3, testedaccording to Example 4, gave the alternating load number of 1,200.

EXAMPLE 6 EXAMPLE 7 Cylinder heads made from the alloy 0.85 7r Mn 4.7%Mg 1.7% Si balance as in Example 2, were tested on the test-bench foralternating thermal stresses according to Example 4 and endured 1,221alternations of stress.

EXAMPLE 8 Cylinder heads of the alloy according to Example 7 with only0.3% Mn, tested on the test-bench for alternating thermal stresses as inExample 4, endured only 430 alternations of stress.

Table 9 Strength properties of the different alloys in the border of thespherical cap of the cylinder heads.

As per Alternating Mechanical properties at 20C example load numberYield Breaking 7( Brmell Stress Strength Hardness kp"/mm kp"/mm kp*/mm01,, HB

' p ponds The further development of the present invention is dedicatedto showing a way of how the ability to endure high thermal stresses,particularly in cylinder heads cast from the aforementioned Al-Mg-Sialloys of the invention, can be considerably improved for obtaining amarked increase of engine operating life, alternating thermal stressendurance and considerably increased durability of sealing surfaces.This is done particularly by increased hardnesses of sealing surfaces,giving also an improvement of the compression chamber seal betweencylinder block and cylinder head. So far, the sealing surfacedurability, which is connected with the Brinell hardness of the alloys,could not alone be considerably improved by concentration increases inthe alloy, without at the same time reducing strongly the ability toendure thermal fatigue in cylinder heads made from the alloys.

Especially for thermally highly stressed pieces, such as engine cylinderheads, it has so far been thought that the thermal treatment shouldconsist only of a kind of stabilization annealing and that this cannotbe improved, but only be deteriorated, by other treatments, particularlysolution treatment alone or a solution treatment, and a subsequentage-hardening. which is customary for all other alloys. It is known thatpiston alloys for the prevention or reduction of increase in volume arehomogenized at 500 C, with subsequent age-hardening, and annealed oncemore at temperatures of 250 C in the softening area, in order to attaincomplete growth resistance and freedom from stresses. However, thesolution annealing treatment is not the rule for piston alloys, and ithas been shown that also an exaggeratedly long annealing at C from 16 to40 hours, without solution treatment, is sufficient for stabilizing orprevention of growth. Beside that, temperatures of approximately 220 Chave also been applied for annealing treatments alone.

The result of these thermal treatments is that alloying components comestrongly out of solid solution. Thereby either maximum Brinell hardnessproperties with strongly decreased elongation properties or else verylow Brinell hardness properties are obtained.

The intended further development of the invention involves subjectingthe castings to either a solution treatment alone or to a solutiontreatment and subsequent age-hardening without exceeding the hardnessmaximum.

Investigations with this process have shown that a considerableimprovement of all properties important for resistance to thermalfatigue, especially sealing surface hardness, is obtained, withoutdisadvantage, with the applied thermal treatment. The results of suchinvestigations are listed in Table 10 and become evident from theExamples of alternating thermal stressing of cylinder heads. Shown arethe Brinell hardness properties and in individual cases strengthproperties in the border of the spherical cap of the cylinder heads. [Iwas found that either a homogenizing or solution treatment must beapplied or a solution treatment with subsequent age-hardening withoutexceeding the hardness maximum of the alloy.

From these results, it can be seen that the investigated alloys showafter the treatment according to the invention considerably higherproperties, particularly for the sealing surface hardness, as comparedwith their original properties, and that they endure at the same timehigher alternating thermal stressings. The Examples show that theBrinell hardness properties after a stabilizing annealing are low.

In view of these results it is shown that cylinder heads treatedaccording to the invention, even those with a higher Mn-content have aconsiderably longer durability and that the sealing surface hardness isincreased. The cylinder heads from such alloys, listed in the followingExamples, particularly Cu-containing alloys, show that the alternatingload numbers are considerably increased by the application of thethermal treatment of the invention. This important improvement was notto be foreseen at the present state of the art.

Table Strengthproperties of permanent mold (gravity die) test barsaccording to the German Air Standard LN 29 531 with a diameter of 22 mmfrom the manganese-containing Al-Mg-Si alloy without and with copperAverage values from two test bars each Mechanical Properties Compositionin Heat treatment a 0' 8,, HB

and quench Winks Cu Be Mg Si Mn Fe Ti kp*/mm k 7, q A oy Designation411/1 0.02 0.004 3.9 0.9 0.85 0.20 0.16 Stabilizing annealin air 10.122.9 10.6 66.5 l2"S65C/H O 10.5 25.1 19.6 68.5 12"565C/H,O 17.8 29.415.8 85 +6"l55C 12"565C/H,O 19.4 29.5 14.1 83 +6"l75C 41l/l 0.84 0.0054.0 0.89 0.85 0.20 0.16 Stabilizing Cu annealing/air 11.4 21.0 3.8 72.5

12"565C/H2O 12,9 2 ,9 & 75 l2"565C/H2O 25.5 33.3 6.2 110 +6"155C12"565C/H-O 25.5 6husroc 2 36.7 8.6 103 p=p0nds EXAMPLE 9 EXAMPLE 11Investigations for cylinder heads of an alloy having a With thefollowing alloy in identical cylinder heads composition according toExamples 9 and 10, the following results were obtained.

0.9 71 Mn 3.9 v. Mg 0.9 7: Si 71 Cu Z M 0.18 '1' Ti t 1.5 7r Si 0.24 71Fe I s Ni 0.004 Be Cu Balance Al '7 Ti Heat treatment and quench h 0.257r Fe 12 565C/Hz 12565C/H,() +6"155C g- 9 ,5 Alternating o I. 0

Heat Stabilizing 12 565 C/H.O 12 565 C/H-,O load number 1751 TreatmentAnnealing z 6"175C HB kponds/mm 80 83 Ahemming Properties from 00.2 13.0kp"/mm 18 2 kp"/mm load number 1642 1700 1930 the border of the 08 27.0kp*/mm 27.2 kp/mm clyinder head 85 10.0 71 8.8 71 HB spherical cap HB 80kp"/mm 83.0 kp*/mm kp"/mm 74 93 102 p ponds p ponds The Brinellhardnesses of cylinder heads made from this alloy were between andkiloponds/mm after stabilizing annealing. EXAMPLE 12 50 EXAMPLE 10Further investigations of cylinder heads made of the Investigations ofcylinder heads made of an alloy with followmg alloy g the followingresults:

0.9 7: Mn 3.9 1 Mg 0.9 7c Si 0.8 1 Cu 0.18 Ti 0.32 Z Fe 0.004 Be BalanceAl.

Stabilizing l2"565C/H O Heat Treatment Annealing l2"565C/H,0 6"175CAlternating load number 1275 1570 2095 HB kp"/mm 7| I04 Properties from00.2 12.0 kp'lmm 16.8 kplmm 27.8 kp/mm the border of the EB 18.4 kp"/mm*32.6 kp"/mm 33.5 kp/mm" s herical cap of 65 2.9 1 5.4 l 6.6 1' tliecylinder head HB 71 kp*/mm 110 kp'lmm 108 kp'/mm p ponds .22..

The results ofthe Examples 9 12 reflect the essence of the invention intwo respects; firstly, the established thermal treatment removes theinfluence of unfavorable higher magnesium contents; secondly, after thesolution treatment, without disadvantage to the ability to endurealternating thermal stressing, the hardness properties can, even with anincrease of the Mgconcentration, be increased considerably, withoutthereby reducing the resistance against alternating thermal stressing ofthe cylinder heads.

As shown by Examples 9 12, a solution heat treatment alone can besufficient, while a subsequent aging can lead to the obtaining of otherdesired properties.

such components further materials with particularly fine structures.This task is accomplished by the invention in such a way that in anAl-Mg-Si alloy, for the indicated purpose, cobalt or chromium or acombination of the two elements act as elements for reducing thesolubility of hydrogen to replace completely or partly the manganesecontent of 0.6 to 2.0% indicated for other alloys of the invention. Thereplacement is to be on the basis of equivaleiit numbers of gramatoms.Preferably at least 0.1% Co and/or at least 0.6% Cr is present. In thismanner, a grain refining of the structure of components is attainedwhich lends to these components additional outstanding properties. Thus,there can be found in the structure in the case of chromium largerislands with very fine Mg Si. Moreover, the resistance of components,e.g. of cylinder heads, made of Al-Mg-Si alloys, which contain withinthe indicated limits besides manganese partly cobalt and/r chromium, isexcellent.

Also vanadium and molybdenum can be used as elements for reducing thesolubility of hydrogen. They replace the manganese content on the basisof equivalent numbers of gram-atoms. At least 0.1% V and/or at least0.1% M0 is preferably present in such alloys.

Table 11 shows the effect of Cr, Co, V, and M0 in alloys of theinvention. Charge Nos. 850 and 2606 are presented for purposes ofcomparison.

TABLE 1 l Strengnth values determined using chill-mold rod castingsaccording to German Aviation Standard (Luftfahrtnorm) LN 29531 with 22in diam; average of three values; influence of Cr, Co, V, and Mo.

Works Analysis in Heat Treatment Mechanical Values Alloy No. 0 0,, H8

or Charge Cu Be Mg Si Mn Fe Ti kp/mm kp lmm 850 Stabilizing (s. Tab.2)n.b. 3.6 1.04 0.22 0.31 n.b. Annealing 7.7 17.1 6.1 54

2606 0.90 0.003 4.4 1.52 0.01 0.17 0.22 Solution Heat 19.7 28.8 6.2 97

Treatment 6 hrs at 175C 0.1% Co 0.88 0.005 4.7 1.45 0.01 0.23 0.19 do.20.1 31.5 8.5 102 Thus, 1n Example 12 where there is a high free Mg con-1t preferred to use technically pure aluminum. Pertcnt, a solution heattreatment alone can give very recentages here1n are 1n percent by welghtunless indispectable properties. In contrast, Examples 9 -11 show that.for a lower free Mg content, an aging in addition to the solutiontreatment can be of advantage. Then, it remains to be noted that, when avery high Brinell hardness is required for sealing surfaces, for examplefor surface 18 in H6. 3, an age hardening can be of advantage as shown,for example, in Example 11.

The present invention also leads to the further development of alloysfor components which are subjected to maximum alternating thermalstresses, particularly for cylinder heads for combustion engines, thematerials for which are based on the Al-Mg-Si alloys of the invention.This further development aimed at finding for cated otherwise.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

1 claim:

1. A high-strength manganese-containing Al-Mg-Si alloy having a freemagnesium content of 1.5 to 4%, said alloy consisting essentially of 0.6to 1.8% manganese, 2 to 7% magnesium, 0.6 to 2.5% silicon, 0.1 to 0.3%titanium, and having been subjected to one of the following steps (a)and (b):

a. a solution treatment up to 565 C maximum;

b. a corresponding solution treatment with subsequent age-hardening attemperatures not exceeding the hardness maximum.

2. An alloy as claimed in claim I, said alloy containing up to 1.5% Ni,up to 3% Cu, up to 0.1% beryllium, and at most 0.6% Fe.

3. An alloy as claimed in claim 1, said alloy containing manganese onlyin the quantities up to 1.2%, magnesium from 3.0 to 4.5%, silicon from0.8 to 1.2%, and copper from 0.2 to 1.0%.

4. An alloy as claimed in claim 1, the magnesium content of said alloybeing from 4.5 to 7.5% and thesilicon content of said alloy being 0.8 to2.5%.

5. An aluminum-magnesium-silicon alloy consisting essentially of 0.6 to4.5% silicon, 2.5 to 11% magnesium, and aluminum, wherein theimprovement comprises l to 4.5% free magnesium and at least one materialselected from the group consisting of manganese at 0.6 to 1.8%, cobalt,chromium, vanadium. and molybdenum, where the sum of the gram-atoms ofmanganese, cobalt, vanadium, and molybdenum lies in the gram-atom rangeequivalent to 0.6 to 1.8% manganese.

6. An alloy as claimed in claim 5, said alloy containing at least oneelement selected from the group consisting of cobalt at at least 0.1%and chromium at at least 0.6%.

7. An alloy as claimed in claim 5, said alloy containing up to 1.5% Ni,up to 0.5% Cu, and at most 0.6% Fe.

8. An alloy as claimed in claim 5, said .alloy containing 3% freemagnesium.

9. An alloy as claimed in claim 5, said alloy containing at least oneelement selected from the group consisting of vanadium at at least 0.1%and molybdenum at at least 0.1%.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,250Dated February 1975 lnventofls) Paul Zimmermann It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Columns 9, 10, 11 and 12 as shown on the attached pages should be added:

Signed and Scaled this sixteenth D 21) 0f September 1 9 75 [SEAL]Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissimn-r uf I aThu/WNW!" 9 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a graph ofalternating load number versus the percentage of free magnesium in analloy.

FIG. 2 is a graph of the percentage of silicon in an alloy versus thepercentage of magnesium and shows the field of free magnesium contentsbetween I and 3%.

FIG. 3 is a cross section through a portion of an aircooled cylinderhead according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred elements for reducingthe solubility of hydrogen in the melt above 700 C are manganese andnickel.

The available results were applied to investigations of cylinder heads.The quality of service to be expected from an alloy used to make acylinder head was measured in terms of alternating load number. which ismeasured as follows.

On a heatable and coolable test stand. those portions ofa cylinder headas are most endangered. being nearest to the combustion chamber. areheated for approximately 60 seconds from a temperature of I to 300 C andthen cooled in 60 seconds to l00 L again. This effects a change of load.The test on the test stand is carried on until crack formation and thenon until the crack has progressed through the wall where it is lo cated.The number of load changes supported by the cylinder head until crackformation and until crackthrough yields alternating load numbers. whichserve as an indicator of the ability to resist thermal fatigue.

FIG. I shows among other things the alternating thermal stress tests ofcylinder heads made of the customary alloy AlMgSSilCu0.5 per Table 7.The cylinder heads of Table 7 were taken from the normal production in aperiod extending over several months. There resulted an averagealternating load number of 716 until crack formation and 769 untilcrack-through.

Cylinder heads cast from the material of the inven- Page 2 tion andshowing a fine grain structurtwere likeuisc tested FIG. I and Table 8show the resulting alternating load numbers. It can be concluded tromthe ll'l' LMlgations that with a silicon content comparable with thecustomary alloy. and with the customary addition at 0.5% Cu. alloys withhigh magnesium contents have a considerably shorter operating life evenwith an additional manganese-alloying. In comparison with the resultsfor the customary alloy (see FIG I and Tables 7 and 8 t. the alloys withhigher manganese content show a distinct improvement. The graph in HG. Ishows an almost linear dependence between alternating load number andmagnesium content and the possibility of a maximum improvement of 100%by the invention The alioy used for cylinder head No. 3 in Table 8 andFIG. I possesses a free i.e.. not present in Mg Si l mag nesium-contentof approximately 5.71'. the alloy of head No. 2 has a freemagnesium-content of 3.77 and the alloy of head No. 1 has a freemagnesiumcontents of only 2.85%. The alloys of heads No 4 and No. S inTable 8 contain only about 0.9! free magnesium. The alloy of head No. 5endures after the additional alloying of manganese considerably higherthermal loading. Comparison with the alloys of Table 7 shows the highthermal stress endurance obtained by the reduction of the free magnesiumcontent. The free magnesium content of the alloys Nos. 4 and 5. being0.9% is very low. The machinability of these alloys was worse on aproduction line. The free magnesium contents should be more than Vi.

The alloys of the invention can also be used as wrought material, if theSi-eontent is at least li All investigations show that the freemagncsiumcontents of the aluminum-magnesium-silicon alloys for obtaininghigh endurance. specially against alternating thermal stresses. shouldbe between 1 and 4.5. prefe rably at 3.0%. a decrease of free magnesiumto less than 1% being possible only for castings that are machined withspecial tools adapted to the alloy. In the presence of more than 0.6% Mnthe preferred 3% free magnesium can go up to about 4.5%.

Table 7 Cylinder Head Analysis in 1' Alternating load No. No.

Mg Si Mn Cu Fe Crack Crackforrnation through I n.b. 709 2 5.06 0 )4 0.360.5 3 0.45 639 670 3 E94 M0 4 940 I050 S 450 640 6 5 I) 0.99 0.36 0.510.44 775 877 7 707 R72 8 574 736 9 M0 66 l0 n.b. J l l 830 H 12 n.h. Il3 5.": 0.95 0.36 0.55 0.43 n.b. 720 I4 n.b. 660 IS (1.). 6'" l6 n b.(Kl Average values 5 i4 096 0.36 U 54 0 44 Ho '1! rib. not preciselydeterminable Page 5 Table 8 (ylmder Head Analysts in .t Alternating loadN Nu Mg Si Mn Cu Fe ll Be Crack (racl.-

formation through I 4 55 0.99 0.91 0.50 042 0.15 0 004 t-tiu I600 ["01500 2 5 Hi0 0.92 0.50 0.32 ti l5 0.004 ttt'ti H90 I200 I224 3 '.'.40.98 0.89 0.55 0.33 0 l5 0.003 n.h lhtl n.b. 335

4 4.4 2.08 0.02 0.!7 0.20 (H5 ll 004 I040 l I00 930 I030 n.b. l [00 S4.3 L88 0.78 0.l5 0 21 015 0.004 I380 i590 I380 i420 I360 MW ".0. notprecisely determinable During the further development of the alloys ofthe invention and of their applicability. it has been established bythermal alternating stress investigations that, within the range of thelimits of the invention. alloys with the following alloyingconstitutcnts have particu- 0.0 0.05! other elements individually. totalhowever 015; maximum Balance aluminum and customary contaminants. on thecondition that only l to 3% magnesium unbound to silicon be contained inthe alloy. A special importance is. in this instance. attributed to theproportioning of the manganese on which the increase of crack resistancein engine operation depends.

The proposed alloy selection results in particularly favora lemechanical properties. Eat all alloys. both those named first. and thoseselected now. yield especially improved mechanical properties and to thepresent time. the best crack resistance against temperature changes. ifthe endangered or highly stressed areas of the cast body are subjectedduring the solidification to a cooling additional to the coolingreceived by other areas of the body. The behavior of alloys free ofmanganesc shows in cylinder heads to 50% of the durability achieved tncylinder heads made of alloys containing manganese.

FIG. 2 shows the range of preferred alloy compositions wherein only I to3% free magnesium (not bound to silicon) is present.

Further illustrative of the invention are the following Examples:

EXAMPLE 1 l ndcr heads of the type illustrated by air-cooled cylinderhead l0 in FIG. 3 from an alloy poor in manganese. having thecomposition 5 2% Mg 1 (Vi Si 0.004% Bt. balance Al and customarycontaminants. were subjected to an alternating thermal stressinvestigation after cooling the permanent mold with about 700 cm H O inthe area of the spherical cap 11. The cooling was carried out by flowingthe water through a metal mold core abutting against the spherical capII and having cylinder inserts protruding into the inlet channel [2 andthe outlet channel 13. The cooling effect pro vided by the cylinderinserts provides an additionally improved microstructure in the web 14.which is the most highly stressed portion of the head. The alternatingload number was approximately 450 for the start of cracking of the webarea between the inlet and outlet channels. Additionally in FIG. 3. axesl5. l6 and 17 are axes of cylindrical symmetry for. respectively. theinlet channel [2. the spherical cap I1. and the outlet channcl l3.

EXAMPLE 2 Cylinder heads of the same alloy as in Example l showed. afterbeing cooled with 3.5 liters H 0 in the same area. an alternating loadnumber of 750.

EX AM PLE 3 Cylinder heads of the manganese rich alloy w th thecomposition L01 Si 0.0049? Be balance Al and customary contaminants.were sub jccted. after cooling as in Example 2. to an alternatingthermal stress. test and -iclded an alternating load numher of LS 0 tocrackthrough.

1. A HIGH-STRENGTH MANGANESE-CONTAINING AL-MG-SI ALLOY HAVING A FREEMAGNESIUM CONTENT OF 1.5 TO 4%, SAID ALLOY CONSISTING ESSENTIALLY OF 0.6TO 1.8% MANGANESE, 2 TO 7% MAGNESIUM, 0.6 TO 2.5% SILICON, 0.1 TO 0.3%TITANIUM, AND HAVING BEEN SUBJECTED TO ONE OF THE FOLLOWING STEPS (A)AND (B): A. A SOLUTION TREATMENT UP TO 565*C MAXIMUM, B. A CORRESPONDINGSOLUTION TREATMENT WITH SUBSEQUENT AGE-HARDENING AT TEMPERATURES NOTEXCEEDING THE HARDNESS MAXIMUM.
 2. An alloy as claimed in claim 1, saidalloy containing up to 1.5% Ni, up to 3% Cu, up to 0.1% beryllium, andat most 0.6% Fe.
 3. An alloy as claimed in claim 1, said alloycontaining manganese only in the quantities up to 1.2%, magnesium from3.0 to 4.5%, silicon from 0.8 to 1.2%, and copper from 0.2 to 1.0%. 4.An alloy as claimed in claim 1, the magnesium content of said alloybeing from 4.5 to 7.5% and the silicon content of said alloy being 0.8to 2.5%.
 5. An aluminum-magnesium-silicon alloy consisting essentiallyof 0.6 to 4.5% silicon, 2.5 to 11% magnesium, and aluminum, wherein theimprovement comprises 1 to 4.5% free magnesium and at least one materialselected from the group consisting of manganese at 0.6 to 1.8%, cobalt,chromium, vanadium, and molybdenum, where the sum of the gram-atoms ofmanganese, cobalt, vanadium, and molybdenum lies in the gram-atom rangeequivalent to 0.6 to 1.8% manganese.
 6. An alloy as claimed in claim 5,said alloy containing at least one element selected from the groupconsisting of cobalt at at least 0.1% and chromium at at least 0.6%. 7.An alloy as claimed in claim 5, said alloy containing up to 1.5% Ni, upto 0.5% Cu, and at most 0.6% Fe.
 8. An alloy as claimed in claim 5, saidalloy containing 3% free magnesium.
 9. An alloy as claimed in claim 5,said alloy containing at least one element selected from the groupconsisting of vanadium at at least 0.1% and molybdenum at at least 0.1%.